Many opuntias are used for wide fences. Any spiny species that grows well should do. I have in use the spiny version of ficus-indica, Austrocylindropuntia subulata and O. leucotricha. The best fences I've seen were of Cylindropuntia tunicata/rosea which is hardy (can be very invasive and not somethi...

I only know of one or two cases were caci fruits are said to be hallucinogenic. Note the "are said". In general it's more a matter of taste, spines etc...

Echinocereus have some of the best tasting fruit I've ever tasted. Some are eaten as vegetables (the plant).

Probably, but some are very acid.

Best nopalitos taste like green beans (most people wont' be able to tell the difference once cooked).